Variable resistors



March 10, 1959 M. BOURNS VARIABLE RESISTORS Filed July 5, 1955 3Sheets-Sheet l 7 March 10, 1959 M. E. BOURNS 2,877,328

VARIABLE RESISTORS Filed July 5, 1955 3 Sheets-Sheet 2 INVENTOR.

22 ZZZ M1 March 1959 M. E. BOURNS 2,877,328

VARIABLE RESISTORS Filed July 5, 1955 5 Sheets-Sheet 3 IN VEN TOR.

2,877,328 Ice Patented Mar. 10, 1959 VARIABLE RESISTORS Marlan E.Bourns, Riverside, Calif. Application July 5, 1955, Serial No. 519,846Claims. (Cl. 201-55) The present invention relates to new and improvedvariable resistors.

During recent years there has been a constant demand for variableresistors which are exceedingly light and small, and which are veryrugged in construction so as to be capable of withstanding a great dealof physical abuse. An object of this invention is to provide new andimproved variable resistors, and in particular potentiometers, havingthese characteristics.

A more detailed object of the invention is, however, to provide a newclass of variable resistors which can be easily assembled by automaticmachines and techniques with a minimum of labor. Those skilled in theart will realize that this is exceedingly important inasmuch aselectrical devices such as resistors are generally very small deviceshaving a large number of individual parts. Formerly, such instrumentswere completely assembled by hand. Obviously, this is a very expensiveand time-consuming procedure.

Another objective of this disclosure is to teach the construction ofvariable resistors which can be satisfactorily utilized as componentparts of larger assemblies with a minimum of difiiculty. In particularit is an object of this invention to provide variable resistors such aspotentiometers which can be readily mounted within a wire cage type ofconstruction by machine. Those skilled in the art will realize that sucha wire cage type of construction is the type of construction covered bythe so-called Tinker Toy project. For this Tinker Toy type of assembly,twelve wires are arranged parallel to one another in a squareconfiguration with three of the wires being disposed on each side of thesquare. Various electrical elements such as, for example, capacitors,fixed resistors and the like are positioned within this cage parallel toone another at right angles to the individual wires.

The features of the instant invention will be best more fully explainedwith reference to the accompanying drawings, in which:

Fig. 1 is a side view of a vention;

Fig. 2 is a cross sectional view taken at line 22 of Fig. 1;

Fig. 3 is a cross sectional view taken at line 3--3 of potentiometer ofthe in- .Fig. 1;

taken at line 7-7 of Fig. 9 is a cross sectional view taken at line 9-9of Fig. 8;

Fig. 10 is a side view similar to Fig. l of a second modifiedpotentiometer of the invention;

Fig. 11 is a cross sectional view taken at line 11-41 of Fig. 10;

Fig. 12 is a cross sectional view taken at line 12-12 of Fig. 10; and

Fig. 13 is a cross sectional view taken at line 13-43 of Fig. 11.

It is to be understood that the accompanying drawings are made so as toclearly illustrate the essential features of the invention; hence, incertain cases they do notrepresent commercial units drawn to scale. Itis possible to modify the various dimensions of the parts shown toproduce any number of different constructions embodying the essentialfeatures of they present invention. Where convenient for purposes ofexplanation and illustration like numerals have been used to designatelike parts.

These essential features are set forth in detail in the appended claims.If desired, however, the invention may be explained by summarizing it asbeing concerned with electrical instruments such as potentiometers orvariable resistors which include: a non-conductive base having an uppersurface; a non-conductive top rotatably mounted upon said base so as tobe spaced from the base, said top having a lower surface positionedparallel to said upper surface; an arcuate resistance strip or elementmounted upon said lower surface about the center of rotation of saidtop; a conductive strip or element electrically connected to saidresistance strip, said conductive strip being mounted on said lowersurface of said top, and including an arcuate portion formedconcentrically with said resistance strip; terminal means located on theupper surface of said base; and resilient contact means secured to saidterminal means so as to engage said resistance strip and said arcuateportion of said conductive strip.

The actual details of the invention as well as the meaning of thevarious terms utilized in the above brief summary are best explained bydirect reference to the accompanying drawings. In Figs. 1 through 4 ofthe drawings there is shown a potentiometer 10 having a non-conductivebase 12 formed of ceramic or other material. This base 12 is preferablyin the shape of a small square wafer having formed along the sides 14thereof a plurality of notches 16 which are designed to hold individualwires such as are employed in the aforenoted Tinker Toy type ofconstruction. Within the center of the base 12 there is formed anopening 18 through which there projects a hollow rivet 20 in such amanner that this rivet extends beyond an upper surface 22 of the base 12in order to hold upon this base a non-conductive top 24. This top ispreferably of a circular form and is of a smaller diameter than thelength of the sides 14 of the base 12, so as to fit entirely within theconfines of the edges of this base.

Around the top 24 there is formed a spacing ring 26 having a knurledouter surface 28. This knurled outer surface is arranged so that it maybe engaged by an appropriate tool or the hand of an individual in orderto rotate the top 24 about the rivet 20. Thus, with the constructionshown the rivet 20 serves essentially as a pivot means serving to mountthe top 24 with respect to the base 12. The top 24 and the spacing ring26 may be formed out of any appropriate non-conductive material such as,for example, a phenolic composition. They may be attached to one anotherby any convenient means such as, for example, an adhesive or the like.

The top 24 includes a lower surface 30 which is positioned parallel tothe upper surface 22 of the base 12 so as to be spaced above this uppersurface. Formed upon the lower surface is an arcuate resistance strip 32having ends 34 and 36 located soas to be centered aboutthe n'vet 20.Also upon the lower surface 30 there is posi- I terminal portion 40 3tinned a first electrically conductive strip 38 having a overlying theend 34 of the resistance strip. This first electrically conductive stripalso includes an arcuate portion 35 concentrically located within theresistance strip 32. A second electrically conductive strip 44 is alsomounted upon the lower surface 30 so that a terminal portion of 46 of itoverlies the end 36 of the resistance strip 32; this second electrieallyconductive strip also includes a second arcuate portion 48 locatedconcentrically to the resistance strip a 32 and the arcuate portion 42.The resistance strip 32 and the electrically conductive strips 38 and 44are preferably formed out of known materials, such as inks loaded withresistance particles and silver inks, by conventional printed circuittechniques. It is hardly considered necessary to describe in detail suchprocedures and materials inasmuch as they are well known to the art atthe present time.

Terminal means 50, 52, and 54 formed out of a conductive printed circuitcompositions such as silver inks are located upon the upper surface 22of the base 12 so as to project to the sides 14 of this base beyond thespacing ring 26. Attached to these terminals 50, 52, and 54 are smallresilient metal contacts 56, 58, and 60, the construction of which arebest seen in Fig. of the drawings. These contacts are formed identicallyso as to each include a bottom 62 adapted to be attached by solder orthe like to one of the terminals 50, 52, or 54, a resilient center arm64 and an upper end section 66. The upper end sections 66 of thecontacts 56, 58 and 60 are designed to bear against resistance strip 32and the first and second electrically conductive strips 38 and 44, sothat as the top 24 is turned about the rivet 20, these contacts engagedifferent portions of resilient strip 32 and the arcuate portions 42 and48. From a detailed consideration of the drawings, it will be realizedthat with this construction the resistance between the contacts 56, 58,and 60 and the corresponding terminals will be varied as the top 24 isturned.

In Figs. 6, 7, 8 and 9 of the drawings, a modified potentiometer 68 ofthe invention is shown which includes a base 12' of the categorypreviously described. For convenience of explanation, the individualparts of this base will not be renumerated in detail. The individualparts of this base and the parts of various other elements which are thesame as in the potentiometer 18 are not enumerated in this portion ofthe description. Such parts are merely designated by the same numeralsas used in the preceding discussion in the same manner in which the base12' is designated.

The potentiometer 68 differs from the potentiometer in that theterminals 50', 52' and 54' employed are of slightly different shape thanthe terminals previously described. However, if desired, these terminalsmay be of substantially the same shape as those indicated in Fig. 2 ofthe drawings. Conversely, the terminals shown in Fig. 2 of the drawingsmay be of substantially the same shape as the terminals shown in Fig. 7.

Attached to each of these terminals 50', 52, and 54 are contact elements56, 58', and 60 as previously described. The contact 56 is designed toelectrically connect an arcuate resistance strip 32' positioned aboutthe rivet to the appropriate terminal 50'.

Upon the lower surface of the top 24 only one electrically conductivestrip 70 similar to the strip 38, is employed. This electricallyconductive strip includes a terminal portion 72 overlying the center ofthe resistance strip 32 so as to engage this strip. It also includes anarcuate portion 74 positioned concentrically with the resistance strip32' about the rivet 20. The contact 58 previously described is alsodesigned to engage the arcuate resister strip 32'. With thisconstruction the two contacts 56' and 58' are intended to engage theresistance strip 32 on opposite sides of the terminal portion 72. Thethird contact 60' is so located as to normally engage the arcuateportion 74 of the electrically conductive strip 70. It is readily seenfrom a consideration of the foregoing description of the modifiedpotentiometer 68 that the resistance between the terminal portion 72 orthe contact 60 and either of the contacts 56' and 58' varies as the top24' is rotated about the rivet 20' during the use of this potentiometer.

In Figs. 10 through 13 of the drawings a second modified potentiometerof the invention is shown which differs from either potentiometer 1and/or the potentiometer 68 in that what in efiect is a doubleresistance strip is utilized so that the entire potentiometer may beturned thereon an arc of slightly less than 360'. It will be noted bythose skilled in the art that various stop means (not shown) mayobviously be employed so as to limit the amount the top 24 may be turnedin order to prevent the contact elements shown in all of thepotentiometers indicated from moving off of the strips they respectivelyengage.

Since practically all of the parts shown in the potentiometer 80 areidentical with the various parts of the potentiometers 10 and 68, likenumerals are used to designate the same parts as previously indicated.Such numerals are, in the Figs. 10 through 13, designated by a doubleprime symbol for convenience.

The potentiometer 8G differs primarily from the potentiometers 18 and 68in that two arcuate resistance strips 82 and 84 are employed togetherwith a center electrically conductive strip 70". This center stripincludes a terminal portion 72 which overlies the resistance strip 84 atapproximately the same point where this resistance strip is joinedthrough a small electrically conductive segment 86 to the resistancestrip 82. With the construction shown the top 24" may be turned so as toplace the contact elements 56", 58" and 60" in engagement with theresistance strips 82, 84 and the conductive strip 76 respectively.

In order that the potentiometer 88 may operate satisfactorily, it ispreferable to form both the resistance strip 82 and the resistance strip84 in such a manner that the change in resistance in each of thesestrips along an arc of the same number of degrees is the same. This maybe accomplished in several ways. One procedure is to use difierentresistance inks for the two different resistance strips. Anotherprocedure is to vary their widths as shown so that the width of theresistance strip 84 is less than the resistance strip 82. In otherwords, when the two arcuate resistance strips in the potentiomcter 80are manufactured of a material having the same resistivity the effectivewidth of this material or cross sectional area of this material isaltered so that the cross sectional area or efiective width of the innerstrip is less than that of the outer strip. If desired, the strips maybe described as having the same resistance per unit angle.

in order to utilize the potentiometers 16, 68 and 80 for the purposesintended, it is necessary to attach various wires or other like means tothe terminals. With the constructions shown part of the upper surfacesof the various bases are always exposed so that wires or the like may bereadily soldered to these terminals. If it is desired to utilize eitherthe potentiometers illustrated as variable resistors, it is onlynecessary to connect two different wires to these units in the obviousmanner.

Those skilled in the art will realize from the foregoing that thepotentiometers shown are very efiicient units for the purposes intendedand that these potentiometers may be readily assembled with a minimum ofdifiiculty by a machine or by hand. They will further realize that thesepotentiometers are very light weight, reliable units, and that theyemploy a different principle of op eration from what has been seen inthe prior related units. Because of this, this present invention is tobe afiorded wide latitude and is to be considered as being base;resilient electrical contact means secured to said limited only by theappended claims. terminal means so as to project therefrom and engage Iclaim: said resistance element and said arcuate portion of said 1. A newand improved potentiometer which comelectrically conductive element assaid top is rotated prises: a non-conductive base having an uppersurface; 5 with respect to said base. a non-conductive top rotatablymounted on said base, 3. An electrical instrument as defined in claim 2said top being spaced from said base, and having a lower wherein: saidresistance element is arcuate in shape; and surface spaced from saidbase; an arcuate resistance wherein said conductive element comprises afirst arcuate element mounted on said lower surface about the centerstrip and a second arcuate strip, said arcuate strips of of rotation ofsaid top; a first conductive element m0untsaid conductive element beingelectrically connected to ed on said lower surface so as to beelectrically conthe ends of said resistance strip. nected to an end ofsaid resistance element, said first 4. A variable resistor whichcomprises: a base; a top; conductive element including an arcuateportion formed a hollow rivet securing said top to said base, so thatconcentrically with said arcuate resistance element; a said top can berotated with respect to said base; a resecond conductive element mountedon said lower sursistance element located on said top adjacent to saidface so as to be electrically connected to the other end base; anelectrically conductive element located on said of said resistanceelement, said second conductive eletop adjacent to said base, saidconductive element being ment including an arcuate portion formedconcentrically connected to said resistance element; contact means onwith said arcuate resistance element; terminal means said base engagingsaid resistance element and said elecloeated on said upper surface ofsaid non-conductive base; trically conductive element; and terminalmeans conelectrically conductive resilient contact means attached nectedto said contact means.

to said terminal means so as to engage said resistance 5. An electricalinstrument of the class described which element and said first arcuateportions of said first and comprises: a square base formed of anon-conductive second conductive elements as said top is rotated withmaterial, said base having a plurality of notches formed respect to saidbase. 2 in the sides thereof to engage parallel mounting rods; 2. Apotentiometer which comprises: a. square non circular top formed of anon-conductive material, said conductive base having a fiat uppersurface; means detop being of smaller dimension than the length of aside fining a centrally located hole within said base; pivot of saidsquare base; a hollow rivet securing said top to means located withinthe said hole so as to project from said base, so that said top can berotated with respect said base past said upper surface; a non-conductivecir- 3 to said base, said hollow rivet extending all the way cular topof smaller diameter than the length of a side through said base and saidtop; a resistance element of said square base having a centrally formedaperture located on said top adjacent to said base; an electricallylocated therein, positioned with said pivot means proconductive elementlocated on said top adjacent to said jecting through said aperture, saidnon-conductive top base, said conductive element being connected to saidbeing spaced from said base and including a flat lower 3 resistanceelement; contact means on said base engaging surface located parallel tosaid upper surface; means said resistance element and said electricallyconductive formed on said top whereby said top may be engaged element;and terminal means connected to said contact and rotated about saidpivot means; an arcuate resistance means. element located on said lowersurface so as to have its center coincident with the center of saidpivot means; References Cited in the file of this patent an electricallyconductive element located on said lower surface, said electricallyconductive element being elec- UNITED STATES PATENTS trically connectedwith said resistance element and in- ,6 3,009 Warner Nov. 27, 1928eluding an arcuate portion formed concentrically with 1,241 RoscntretcrOct. 12, 1948 said arcuate resistance element; electrically conductive,682 Tellkamp July 11, 1950 terminal means located on said upper surfaceof said 7 44 R n eta! 1951

